TW makes more sense in it's 1st and 2nd gen designations. What (in my mind) deifnes the differences is the body styling and engines available. From 95.5-04 you had the same basic body stylings with some minor changes in the front grill. The only major change that was really made was the introduction of the DC in 01. From 05 to present there hasn't been any body styling changes.

You had three motor configurations through out the 1st Gen years; 2.4, 2.7 and the 3.4. The 2nd gen years have two; 2.7 (next gen of the original 2.7) and the 4.0.

well, technically the 96-04 are 1st gen TACOMAs and 05+ are 2nd gen TACOMAs. But, there were the 73-85 pickup(1st gen truck), the 86-95 trucks(2nd gen trucks) so in that sense the 1st gen Tacoma is a 3rd gen truck and the 2nd gen Tacoma is then a 4th gen truck. I think that makes sense....

Like Relentless said, the Tacoma name was not used in North America until 1995, that's the 1st gen which ran through the 2004 model year. In 2005, the re-engineered Tacoma (Motor Trend Truck of the Year) was introduced, that's the 2nd gens. Anything 1994 or older is considered a Hilux (or "Toyota truck" lol). That is my understanding of the North American Toyota truck marketing and model designations. See http://en.wikipedia.org/wiki/Toyota_Tacoma